1. Field of the Invention
This invention relates to a process for preparing an antithrombogenic polymeric material.
2. Description of the Prior Art
In recent years, polymeric materials have come into use in the field of biomedical materials. The use of polymeric materials at sites directly in contact with blood, for example, as vascular prostheses, catheters, artificial kidneys, artificial hearts, lungs and sutures, presents a problem of thrombus formation. Thrombus formation means the conversion of fibrinogen in the blood ultimately to fibrin through a series of complicated enzymatic reactions involving many coagulation factors. Simultaneous with the formation of fibrin in blood coagulation, the fibrin formed continuously dissolves in a fibrinolytic system with an equilibrium being maintained.
Past development and research on antithrombogenic materials are based mainly on a study of the blood coagulation system, and have been directed to the inhibition of the conversion of fibrinogen to fibrin by applying heparin, which acts as an inhibitor for the blood coagulation system, to the surface of the material. Very few prior attempts have started from the fibrinolytic system.
U.S. Pat. No. 3,625,745 discloses a process for forming a thin, continuous adherent coating on a substrate by surface photopolymerization of a synthetic fibrinolytic compound, and an antithrombogenic article. The thus-produced article exhibits some degree of antithrombogenic character, but certain problems arise. For example, it is impossible to coat the surface of an article having a complicated shape or the inside surface of a narrow tube using surface photopolymerization. Furthermore, since the strength of the bond between the polymeric film obtained by surface photopolymerization and the substrate is weak, it is difficult to maintain the antithrombogenic character for long periods of time in the blood stream.